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Engine Tuning Tips - Ted Sander Taken from the SPMRC message forum. |
Author: Ted Sander (---.badplace.net)
Date: 05-22-01 23:03
OK, I'll wade in with a reply. Generally starting at about 2 1/2 turns
out from fully closed would be a place to begin. Starting a new engine
is the worst. Once you get it close everything really does get better.
Have the engine in the plane, with a working throttle. Or, if on a
test stand that's firmly anchoered down, rig up a way to control the
throttle without getting near it (a pushrod clipped to it with a
clevis works well).
Don't clip on a battery yet. Put your thumb over the carburator, and
flip the prop a few times to suck fuel up the fuel line (you should
see it), and to prime the engine (your thumb should be a little
wet). Now attach your battery.
Make sure the throttle is only open about 10 to 20%. Starting an
engine at full open can be very dangerous!
Grab the prop hard with your fist, and slowly turn it over against the
compression. You should feel a "kick" as the piston goes over the
top. May not always happen, but if you do feel it, it indicates your
engine is ready to go.
If the engine is really hard to turn over, disconnect your battery,
and see below about flooding. DO NOT try to use an electric starter on
it if it is hard to turn over!
Now flip the prop smartly in the direction of rotation
(counterclockwise as you face the engine). Or, better, use an electric
starter. You may have to do it several/many times before it starts.
If your arm is getting tired from flipping, time to check for
flooding. Take off the battery. Turn the engine so the muffler is
toward the bottom, with the outlet slightly pointed down. Turn the
prop over slowly several times. If fuel pours out of the muffler, you
were flooded! Keep turning slowly till nothing comes out. If you feel
lucky, try the above starting proceedure again, but this time don't
choke the engine with your thumb.
Still no go? Check again for flooding as above. Then take out your
glow plug. It should be dry. If not, or just for luck, rapidly spin
the engine with no plug in it. Watch out for the forceful spary of
fuel out of the glow plug hole! Repeat until nothing sprays out. Find
the copper washer that blew off into the grass (because you forgot
about it when you pulled the plug!), and put your glow plug back
in. Clip your plug to your battery to make sure it glows before
putting it back in.
Try again.
Try it again, this time with less priming than the first time.
Eventually, it will try to run. If it just barks and quits - or goes
for just a few seconds, slowing down, and probably spitting fuel out
of the carburator, before quitting, screw the needle valve in 1/2 turn
and try again. It may be flooded again.
Keep trying. Will probably be better than the last time. If it still
won't keep running, screw in the needle valve one more 1/2 turn. If at
this point, it still won't go - bring it out to the field, call an
instructor, or get help some other way.
Whew! More than likely, you've got it running by now.
WARNING! The biggest damage you can do is by running the engine too
lean, which means too little fuel/oil going through it to provide
adequate cooling. Resist the temptation at the beginning to screw the
needle valve in "to see how fast it'll go".
Once started, open the throttle fully. If it dies, see the note above
about screwing in the needle valve. Get help if you reach the 1 1/2
turn point, and it still won't stay running.
It should be running sloppy rich - spewing fuel/oil over
everything. Maybe still spitting raw fuel out of the carb. You should
be able to put your hand a little behind the muffler and not get burnt
by the exhaust, but it will get quickly coated in oil - which is good!
It will be pretty hot - but not painfully so. Turn out that needle
valve right away 1/4 turn if you have doubts. If it stops, oops, too
far. Turn it back in and restart.
Run an ENTIRE tank through it without touching the needle valve. Use
your throttle to slow down and speed up the engine periodically. Do
not try to make it go too slow - it will probably quit because we
haven't worried about setting the idle yet. Just slow it down so it
has a chance to cool off between the fast periods. NOTE: these
instructions are for a ringed engine like the LA .40 An ABC
(non-ringed) engine needs a variation of these instructions.
Run another tank of fuel through it, with fewer periods of slower running.
Do this with two more tanks. The last should be run with the engine at
full throttle for the entire time.
Oh no, not done yet! NOW you can start fine adjusting the needle
valve. Turn it in slowly, listening for the engine to change in
pitch. You'll find a point where it rapidly changes from blubbery rich
to a high pitched consistent whine. Stop there, and turn the needle
back out two to three clicks. Going farther risks running it too
lean. Ideally, you want it to be just at the transition point of going
from blubbery ("4-cycling") to consistent ("2-cycling"). Pointing your
planes nose up will result in it breaking into a 2-cycle run, pointing
the nose down will put it back to 4-cycling.
Run two more tanks through it like this.
Finally, you can read my other posts about adjusting the idle - and do
the same for yours.
A ringed engine really isn't broken in until it has had four or more
gallons of fuel through it! And, the initial breaking in is critical
to long life. After the above, your engine will be good enough, and
broken in enough, to fly. Just continue to be real cautious about
running it lean, and it will last for years.
- Ted Sander
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